I found this example but it... doesn't work.
Can an Opera Dev please update this tutorial to work with the current bookmarks implementation, since that changed? All I get is a blank window.
As for moving tabs to the bottom of the browser... it looks like Chrome Devs pretty much said "no" to all layout customizations in the past several years. I don't give a flying patootie about my background image, I want to change my browser layout. I hope the Opera team is able to change the code enough to allow for layout changes.
Also, I wish I could put those extension buttons on the left side of the browser...